Tom Mellor’s record-breaking 1969 Triumph Trident T150
(Page 3 of 4)
July/August 2009
By Alan Cathcart
More mechanicals
“It started out life as a 1969 bike, but I don’t know what year you’d call the engine that’s in there now, because I get new original crankcases wherever I can,” Tom says. “It’s still a 750 rather than an 850, though, because that’s what I bought, and you race what you have.”
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Tom has retained the original Trident forks and runs a rigid rear suspension, sheeted in the rear wire-spoked wheel with aluminum to reduce drag, and uses a rear disc brake matched by a Yamaha TZ250 twin-leading-shoe drum up front that’s had some work done on it. “I take the shoes out and put 1/2-inch aluminum discs in there,” Tom explains, leaving him with a dummy brake drum. “It’s better than having a disc brake hub on the front because only 25 percent of the spokes are exposed, and weight isn’t an issue.”
Indeed, the final step on the chassis was to add a 75-pound lump of lead just in front of the rear wheel, a common Bonneville tuning trick aimed at delivering extra traction. This bumped the Triumph’s weight up from 339 pounds in road racing form to around 450 pounds, complete with streamlining.
Before preparing the 750cc T150 3-cylinder engine for record breaking on the salt, Tom sourced a close-ratio 5-speed gearbox from the leading BSA/Triumph triple competition specialists in the U.K., P&M Motorcycles, which he matched to a standard chain primary drive. Tom runs a conventional racing clutch, after the lightened aluminum one he built got warped: “It’s all those road racing hole shots, I guess!”
Prior to his Bonneville run, Tom spent an entire week carefully lightening the crank (by 10 pounds) on a lathe, followed by shot peening and fitting a P&M high-volume oil pump. He uses Carrillo rods with Omega pistons, and valves with 6mm stems carrying R&D springs and titanium spring caps, operated via Johnson cams and lightweight 4130 steel pushrods. “You don’t want to go any bigger on valve sizes, because Triumph valves are plenty big enough,” he says. “I milled out the cylinder head, and got the intakes slightly more angled for extra downdraft, then I ported it myself and fitted 32mm Amal carbs, which aren’t even smoothbores and especially not Mikunis, so there’s extra performance we could have right there. I was going to go to 34s, but I didn’t have time to test them on the dyno.”
The reworked, ported cylinder head has a high, 14.3:1 compression, which means running 112 octane fuel (still OK for the pump gas rule) and 10mm spark plugs moved a little closer to the center of the piston. “I don’t run two spark plugs, because it doesn’t make any difference,” Tom states. “Now it revs to 9,300rpm, and two weeks ago when I checked it before leaving, it gave 82hp at the rear wheel at about 9,000rpm. In fact, that fastest run I did, I was doing 9,500 all the way down the long course, and we had it geared just right. The first sprocket we chose pulled 171mph at max rpm, then we dropped it two teeth and pulled 180. Dropped two more teeth, and would still only pull 180 — so we got the old girl going as fast as she’ll go.”